1. Field of the Invention
The present invention relates to a ball quantitative supply system for supplying a fixed quantity of balls of a ball screw used, for example, in a steering mechanism of an automobile to a work such as a nut screw.
2. Description of the Related Art
In some automobile steering mechanisms, ball screws are used. The ball screws are arrangements in which steel balls (hereinafter simply called "balls") are disposed between helical grooves of nut screws and helical grooves of shaft screws. The nut screws are axially movable by rolling the balls by rotational forces of the shaft screws connected to the steering wheels.
For assembling the ball screws, the balls are first supplied to the nut screws, whereafter the nut screws and shaft screws are assembled to form a unitary body.
An example arrangement for assembling such ball screws is disclosed in Japanese Patent Kokai (Laid-Open) Publication No. SHO 59-29867 entitled "SYSTEM FOR AUTOMATICALLY DISTRIBUTING, FEEDING AND PUSHING IN BALLS". In the disclosed system, balls are distributed and supplied from a ball distribution-supply apparatus to a ball push-in apparatus via a plurality of lead pipes. The supplied balls are sent into respective guide apertures formed in the ball push-in apparatus. The balls placed in the guide apertures are pushed into a respective space defined by a helical groove of a nut screw and a helical groove of a shaft screw and placed thereat. The balls are counted by a counter as they are fed from the ball distribution-supply apparatus to the ball push-in apparatus.
However, in the above-described system, an expensive counter is employed to detect the number of balls fed, thus increasing the general cost of the system. Further, since the balls are supplied and discharged through the same guide apertures, the requisite operations are liable to become complicated, whereby erroneous actions are encountered.
The balls are supplied to the nut screws as final works by means of a ball feeder. A typical ball feeder has a casing for accommodating a multitude of balls. A bottom portion of the casing is configured to be an inverted conical trapezoid (in the form of an inverted flask) having a linear cylindrical portion. At a border between the linear cylindrical portion and the inverted conical trapezoid portion, there is provided a ball discharge port. A ball supply port is provided at a lowermost end of the linear cylindrical portion. The diameter of the ball discharge port is slightly larger than the outer diameter of the balls. Thus, by imparting vibrations to the casing, the ball feeder can send out the balls within the casing one by one sequentially from the ball supply port through the ball discharge port.
In this ball feeder, however, since an upper part of the ball discharge port is diverging upwardly, it often happens that two balls get stuck between an upper part of the discharge port and the inner wall surface of the casing by mutual locking engagement of the balls. As a result, inconveniences are experienced such that the balls may not be discharged out from the discharge port.
Reference is now made to FIG. 15 hereof showing the general arrangement of a typical conventional ball quantitative supply apparatus. The ball quantitative supply apparatus 100 is comprised of a ball feeder 101 for sequentially sending out balls, a first shutter 102 disposed downstream of the ball feeder 101 for opening and closing a flow passage of the balls, a counter 103 disposed downstream of the first shutter 102 for counting the balls, a receptacle 104 disposed downstream of the counter 103 for receiving a predetermined number of balls, and a second shutter 105 disposed downstream of the receptacle 104 for opening and closing the flow passage of the balls.
The balls accommodated within the receptacle 104 are fed to a work 106 such as a nut screw.
In the ball quantitative supply apparatus 100, however, since the ball feeder 101, counter 103, receptacle 104, etc. are interconnected by tubes 107, the ball quantitative supply apparatus 100 inevitably becomes large in size.
Further, the balls fed to the counter 103 become excessive in number or fall short unless the opening and closing actions of the first shutter 102 are made at precise timing.
Moreover, it may not be known with certainty whether the balls are securely supplied to the work 106 by only opening the second shutter 105 to send the balls to the work.
Reference is now made to FIG. 16 in which the general arrangement of a ball quantitative supply apparatus 110 which is an improved version of the ball quantitative supply apparatus shown in FIG. 15. The improved ball quantitative supply apparatus 110 is comprised of a base or body 112 having a rotary block 111, an air cylinder 113 for effecting the rotation of the rotary block 111, a ball feeder (not shown) for feeding balls 114 to the rotary block 111, a ball detector 115 for detecting the number of the balls 114 within the rotary block 111 and a ball discharge mechanism 116 for discharging the balls 114 held in the rotary block 111.
For feeding the balls 114 to a work 117 by the ball quantitative supply apparatus 110, the balls 114 are firstly sent out from the ball feeder to a ball receptacle 111a of the rotary block 111 via a ball receiving aperture (not shown) formed in an upper plate 118. Then, a magnetic valve 119 is operated to actuate the air cylinder 113 by a source of air supply 120 to thereby rotate the rotary block 111. By levelling rotation of the rotary block 111, balls (not shown) retained in the ball receiving aperture of the upper plate 118 positioned upwardly of the ball receptacle 111a are cut off and separated from the balls retained in the ball receptacle 111a, thus leaving a predetermined number of the balls 114 in the ball receptacle 111a.
By further rotating the rotary block 111, the ball receptacle 111a containing the balls 114 is positioned at the ball detector 115.
Next, a magnetic valve 121 is actuated to supply air from the source of air supply 120 to the air cylinder 122 of the ball detector 115. A piston rod 122a of the air cylinder 122 is descended until a lower end of the piston rod 122a is place in abutment against an uppermost one of the balls 114 within the ball receptacle 111a. The height of the piston rod 122a at this time is detected to ascertain that a predetermined number of balls 114 is accommodated within the ball receptacle 111a.
Continuously, the magnetic valve 119 is again operated to rotate the rotary block 111 by the air cylinder 113 so as to move the ball receptacle 111a to the ball discharge mechanism 116. Then, a magnetic valve 123 is operated to cause an air cylinder 124 of the ball discharge mechanism 116 to contract. By contraction of the air cylinder 124, push rods 125 connected to a piston rod 124a of the air cylinder 124 are lowered to be introduced into the ball receptacle 111a so as to push the balls 114 within the ball receptacle 111a into the work 117 through a ball discharge aperture 126a of a lower plate 126.
The improved version ball quantitative supply apparatus 110 is rendered small in size, because the ball feeder, ball detector 115, ball discharge mechanism 116, and so forth are unitarily assembled without using tubes.
Also, by rotating the rotary block 111, a predetermined number of balls 114 can be securely obtained, whereby the relevant control becomes easy.
In addition, since the balls 114 are pushed into the work 117 by the respective push rods 125 within the ball discharge mechanism 116, the balls 114 can be fed into the work 117 securely.
However, in the above-described improved version ball quantitative supply apparatus 110, it is necessary to prevent the rotary block 111 from rotating when the push rods 125 of the ball discharge mechanism 116 are inserted into the respective ball receptacles 111a of the rotary block 111. Thus, sensors 130a, 130b are used to detect the expansion/contraction position of the piston rod 113a of the air cylinder 113. Similarly, sensors 131a, 131b are employed to detect the expansion/contraction position of the piston rod 122a of the air cylinder 122. The expansion/contraction position of the piston rod 124a of the air cylinder 124 is detected by sensors 132a, 132b.
Position confirming section 134 confirms the position of each cylinder based on detected signals output from each sensor and sends the confirmed data to a control section 135. Based on the confirmed data, the control section 135 controls the magnetic valves 119, 121, 123 to operate the air cylinders 113, 122, 124. Thus, the control involves complicated conditions which may lead to misoperations.
To this end, it is demanded that a single switch be capable of operating the cylinders to thereby prevent misoperations liable to occur during operation of the cylinders.